The present invention relates generally to fiber optic cables and, more particularly, to self-supporting fiber optic cables.
Fiber optic cables can be employed in a variety of applications including the transmission of voice, video, and data. Fiber optic cables can be installed either in conduits that are disposed within the ground, or aerially by being strung between utility poles or the like. Self-supporting fiber optic cables can include both optical fibers as well as strength members for providing mechanical support for the aerially installed cable.
Self-supporting fiber optic cables typically include a strength member in the form of a messenger section supporting the fiber optic cable, and a carrier section that includes optical fibers, or optical fibers and electrical conductors. One type of self-supporting fiber optic cable is a xe2x80x9cfigure 8 xe2x80x9d configuration. A xe2x80x9cfigure 8 xe2x80x9d self-supporting fiber optic cable includes a pair of cable sections connected by a web, wherein the messenger section forms one of the sections and the carrier section forms the other cable section. The web joining the messenger and carrier sections typically extends continuously along the length of the cable. Plastic components of a cable have a significantly greater coefficient of thermal expansion than the glass fibers. With changes in temperature, the plastic components may elongate or contract. The strength members in the messenger section help limit the amount of elongation and contraction that can take place by virtue of the connecting web that joins the carrier section to the messenger section.
The carrier section can have an overlength with respect to the messenger section. See, for example, U.S. Pat. Nos. 4,662,712 and 4,883,671, the contents of which are incorporated by reference herein.
In some field applications of figure 8 cables, the messenger and carrier sections are separated from each other over substantial lengths. For example, it may be desired to install the carrier section alone down the side of a utility pole to a repeater or other device. To accommodate such uses, figure 8 cables have required respective strength members in both the messenger carrier section.
One aspect of the present invention presents a fiber optic cable having a messenger section, the messenger section having at least one strength member and a jacket surrounding the strength member. The cable includes a carrier section, the carrier section being free of strength members and at least one optical fiber disposed therewithin, and a web connects the respective jackets of the messenger and the carrier sections.
Another aspect of the present invention presents a fiber optic cable having at least one optical fiber disposed within the jacket, the optical fiber being at least partially disposed along a path and having an EFL of about 0% to about 3.2% at unstressed room temperature conditions.
Another aspect of the present invention presents the combination of a carrier section not including a strength member, and the optical fiber being at least partially disposed along a curved path defined by a surface having an inside diameter between about 3.0 mm to about 13.0 mm, the optical fiber having an EFL of about 0.6% to about 3.2%. Cables according to the present invention can have connecting webs of varying lengths to control elongation of the carrier section.
Another aspect of the present invention presents a fiber optic cable having a messenger section, the messenger section having at least one strength member and a jacket surrounding the at least one strength member. A carrier section is connected to the messenger section by a series of webs, the webs having a general axial length L, with windows defined between the webs, the webs having a general axial length W, the L:W ratio preferably being about 1:1 to about 50:1. Alternatively, the L:W ratio can be about 0.25:1 to about 0.95:1.